In an internal combustion engine, engine performance is influenced significantly by the temperature of the fuel used thereby. Elevated temperatures decrease fuel density, which makes combustion less efficient. Additionally, fuel mass droplet size decrease with fuel density, as does flow rate, which results in less spray penetration.
Today's diesel engines, especially those used in class 6, 7, and 8 trucks, have a very high injection pressure. This high pressure causes the fuel to become heated to undesirable temperatures. An injector pump pressurizes fuel to the injectors. The injectors only use 10-15% of the fuel that is provided to the injectors. The remaining 85-90% of the fuel is returned to the tank at a lower pressure, but still at an elevated temperature. This is not an insurmountable problem until the tank temperature or the fuel temperature increase beyond approximately 150.degree. F. At or beyond this point, various problems occur within the fuel. Also, its combustion efficiency may decline. This is a major truck industry concern which has not yet been solved satisfactorily through conventional cooling methods.
The primary problem with fuel cooling is that one cannot mount an air-to-fuel cooler in the front of the vehicle or in the main cooling air stream due to the possibility of leaks or front-end collisions which may cause leaks to occur. This would be a simple and inexpensive means to cool the fuel, but is not practical or safe.
It is undesirable to use conventional outlet water from the engine cooling system because the temperature of the radiator typically exceeds 150.degree. F., even at the outlet. For heat transfer to occur, there must be a significant temperature differential between the fuel being returned to the tank and the water being used to cool it.
Another conventional cooling alternative would be to use the air conditioning system. This too has some drawbacks because all trucks do not come equipped with air conditioning.
During winter conditions it may become necessary to warm the fuel, especially during engine start up. In cold environments, diesel fuels become jelled and may cause fuel systems to freeze up. Conventional cooling methods described above do not provide for heating fuel when necessary.
Representative of prior art approaches to the above-noted problems are found in the disclosures of U.S. Pat. Nos. 4,036,182; 4,924,838; 4,898,141; 5,368,003; 5,251,603; and 2,994,331.